In 1996, Nichia Corporation developed a blue-light InGaN light emitting diode (LED) to gather with a yellow-light Ce-doped yttrium aluminum garnet (YAG:Ce) phosphor powder using cerium as a light emitting activator to form a white-light light source and unveil the white-light LED market. White-light LED has the advantages of energy saving and environmental protection over traditional light sources and complies with the global development trend of green lights. At present, white-light LED is considered as the illumination light source of the 21st Century and one of the severe competitions for the business opportunity among world's major optoelectronic semiconductor manufacturers, and the industrial values and environmental protection effects derived from the white-light LED are immeasurable.
Compared with the white-light LED adopting the blue-light LED together with the YAG:Ce phosphor powder, the ultraviolet light emitting diode (UV-LED) using 360˜400 nm ultraviolet as an excitation source and conforming with red, green and blue phosphor powders to form a white light having a higher light emitting efficiency and a better color rendering. However, the highly efficient red, green and blue phosphor powders applicable for ultraviolet light is not easily found in the market, and it is necessary to take the efficiency of different powders into consideration for the actual process of packaging white-light LED, and thus the level of difficulty for mixing powders become higher, and the prior art requires further breakthroughs for practical applications.
At present, alkaline-earth silicates compounds are primarily used as a phosphor powder for the excitation of blue light or ultraviolet light, and many manufacturers including OSRAM, GE, Toyota Gosei, Tridonic, and Intermatix have adopted these compounds for the manufacture, and alkaline-earth silicates compound related literatures and patents are described as follows:
The content of (Ba, Sr, Ca)2SiO4:Eu2+ disclosed [J. Electochem. Soc: Solid State Science. 115, 1181-1184 (1968)] by a Thmoas group is the earliest alkaline-earth silicates compound used as a phosphor powder, and its host lattice is a solid solution of (Ba,Sr,Ca)2SiO4, and its light emitting activator is bivalent europium (Eu2+), but this journal did not teach its use for the excitation of LED. Thereafter, the content of (Ba,Sr,Ca)2SiO4:Eu2+ disclosed by GE in U.S. Pat. No. 6,621,211 is the earliest phosphor powder of alkaline-earth silicates compound used for the excitation of LED, and its activator is also a bivalent europium (Eu2+), and the method of producing white light is achieved mainly by exciting the ultraviolet light; and the 360˜420 (nm) LED is excited by the phosphor powder of at least three colors: red (R), green (G) and blue (B). And then, Toyota Gosei, Tridonic optoelectronic GmbH and Lite GBR, Leuchstoffwerk Breitungen GmbH jointly developed an ultraviolet (UV) white-light LED, and patents were issued to U.S.A. and Taiwan (including U.S. Pat. Nos. 6,809,347B and 6,943,380B, and TW Pat. No. 533,604B). The contents disclosed in the patents include one of the alkaline-earth silicates compounds excited by a bivalent europium (Eu2+) or a mixture of the following compounds:
(a)(2-x-y)SrO.x(Ba,Ca)O.(1-a-b-c-d)SiO2.aP2O5bAl2O3cB2O3dGeO2:yE2+, wherein 0<x<1.6, 0.005<y<0.5, x+y≦1.6, 0<a, b, c, d<0.5;
(b)(2-x-y)SrO.x(Ba,Ca)O.(1-a-b-c-d)SiO2.aP2O5bAl2O3cB2O3dGeO2:yEu2+, wherein 0.01<x<1.6, 0.005<y<0.5, 0<a, b, c, d<0.5.
The aforementioned phosphor materials can be used for exciting blue light or ultraviolet light to radiate yellow-green, yellow or orange spectra, and the color temperature of the white light and the color can be adjusted by changing the proportion of variables.